Bearings - 2021-11-15
Unforeseen bearing failures in production-critical machines and equipment can prove extremely costly in replacement parts, labour and downtime, all of which have a negative impact on bottom-line profitability. This problem becomes worse in contaminated environments, such as those prevalent in steel manufacturing, which is why increasing numbers of steel plants are turning to the advantages offered by NSK’s long-life Super-TF spherical roller bearings. Manufactured from a specially developed, proprietary material, these bearings are able to increase service life and uptime significantly.
NSK Super-Tough (Super-TF) bearing steel is a proprietary material that is not only ideal for very high load applications, but has a proven ability to reduce surface-originated flaking from contaminated lubricant.
Bearings in the steel industry often have to operate under conditions where metal particles or debris can easily contaminate lubrication. These contaminants create dents in the rolling surfaces of bearings, where stress concentrated around these dents eventually leads to cracking and surface flaking.
NSK research revealed that a high level of retained austenite is an extremely effective way to reduce stress concentration around surface dents and prolong service life. TF technology in general is a unique heat treatment process to optimise the level of retained austenite in bearing materials. However, austenite itself has a soft microstructure, so to meet the need for greater hardness with a higher level of retained austenite, NSK developed a technique to reduce the diameter of carbide and carbonitride particles in comparison with those present in standard carburised bearings.
The resulting Super-TF bearing steel, with its particular chemical composition and special heat treatment process, offers impressive service life. In 2017, the test house DNV GL certified that, when Super-TF material is used, it is possible to improve the basic dynamic load rating in roller bearings by 23%. This increase equates to an effective doubling of fatigue life in comparison with bearings made from standard steel.
Among those able to support the proclaimed benefits is a steel manufacturer that was experiencing bearing failures (24040 spherical roller bearings) on its cold rolling mill every 3-4 months. NSK engineers analysed the failed bearings and grease samples as part of its AIP Added Value Programme, discovering that the rolling mill’s highly contaminated operating conditions were behind the unexpected bearing failures, costly unplanned shutdowns and reduced production ratios.
The expert team from NSK recommended the adoption of Super-TF spherical roller bearings to combat debris contamination in the lubricant. After a four-month running trial, the steel plant returned the bearings to NSK’s laboratory for inspection. An X-ray fatigue analysis revealed a residual life of 29-50 months thanks to the superior wear resistance of Super-TF bearings.
For the past few years, the steel plant has been replacing its rolling mill bearings only once a year during scheduled maintenance, leading to significant savings in replacement bearing, downtime and maintenance costs.
Picture 1): NSK Super-TF spherical roller bearings provide long service life in conditions where lubrication is easily contaminated. Photo: sspopov/Shutterstock
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